1. Field of the Invention
The present invention relates to filter assemblies for filtering a liquid, such as frying oil, and associated valve assemblies for connecting the filter assemblies with the sources of the liquid.
2. Description of Related Art
Many food products served in retail restaurants are fried in cooking oil or shortening either at atmospheric or elevated pressures. Many of such food products, such as chicken, seafood or vegetables are breaded before being placed in hot oil for frying. The breading is usually a granular wheat product loosely bound to the food by moisture and egg albumin so a variety of particles thereof of different sizes tend to become unattached during the frying process. At first these pieces float, but after substantial moisture is cooked out of them, they sink, falling to the bottom of the fry pot of the fryer where they burn to discolor and impart a burnt taste to the oil. The burnt particles encourage an early breakdown of the cooking oil. The burning occurs even when the fry pot is designed to have a cool sump because the action of frying causes turbulence that keeps the oil at near the same temperature throughout the fry pot. For this reason many commercial food fryers are equipped with an oil filter, which is used to remove the breading particles from the oil after a certain number of frying cycles. Typically this type of filter requires the fryer to be off-line while filtering. The fryer is usually emptied into a lower chamber where the filter is located. Food can not be cooked during this process. The actual number of cycles may depend on the type and characteristics of the breaded food being fried. For example, the filtering of the cooking oil may be accomplished every three to six frying cycles.
Although some filter systems require that the oil be cooled to almost room temperature because of the filtering agents used, filtering is generally performed with the oil at or near normal frying temperatures. Typical oil filtering systems include a drain valve attached to the lower surface of the fry pot. A filter pan is placed underneath the drain valve and the valve is opened. The hot oil then pours into the filter pan with the operator taking care to avoid splashing that can result in severe burns. Even when the operator is careful, splashing can occur, so it may be preferred that the operator take the time to dress in protective clothing prior to the commencement of the filtering process. Such protective clothing commonly includes oil and heat resistant gloves, an oil and heat resistant apron, oil and heat resistant boots, and safety glasses.
Once the oil starts to drain, various scrappers and brushes are used to clean the sides of the fry pot and the electric heating element or gas flame tubes. When all of the cooking oil is drained and the fry pot is partially clean, the drain valve is closed and the hot oil is pumped back into fry pot until it is about ⅓ full. This clean oil is then used to thoroughly wash the sides of the fry pot, after which the oil is again drained and passed through the filter to remove any particles that might have been dislodged during the cleaning operation. The clean oil is then pumped back into the fry pot. After multiple filterings, the number of which are dependent upon the filter and the product accumulating therein, the filter media must be changed. Generally this is done after the oil has been pumped back into the fry pot and the filter has had an opportunity to cool. The whole filtering operation even in a highly automated food fryer can take as much as half an hour per frying pot, during which time the fryer is out of production. In filtering systems where the oil must be cooled prior to filtering, the fryer may be out of use for as much as four hours.
As mentioned above, particulates or “dirt” in the filter encourages the breakdown of the oil and shortens the usable life of the oil. Once the oil is unusable it must be discarded and replaced. It is believed that if the oil is continuously filtered, the life of the oil can be extended. Therefore some continuous filters have been developed. However, the known continuous filters are relatively expensive such that these filters are only economical to large poultry producers and large retail fried food producers and out of reach of many operators. Also, the known continuous filters require pressurized air which is often not available in locations, such as restaurants or other retail establishments.